The integrity of a computer network""s physical layer is critical to its proper operation. While much attention is directed to the operation of the computer-nodes and the network communications devices, e.g., hubs and switches, the relevance assumes proper behavior at the physical layer. For example, in ubiquitous 10Base2, 5, T, and 100BaseT networks, a number of physical layer problems lead to improper operation. Damage to the cabling creates impedance discontinuities in the conductors, which cause signal reflections. This can impair the proper signal transmission, decoding by the nodes or network communication devices, or collision detection, for example. Further, the length of the links can undermine the shared usage of the transmission media. Some protocol specifications, such as the inter-frame gap, are defined based upon the time needed for a given communication event to propagate throughout the entire communication network.
Time domain reflectometry (TDR) techniques have been used to analyze and validate computer networks at the physical layer. The basic process involves generating a predetermined, TDR, signal, such as an impulse or step function, on the conductors of the computer network. At the point of injection, a signal analysis device, such as a digital sampling oscilloscope, is used to monitor the computer network conductors for reflections of the signal. These reflections are induced by impedance discontinuities along the computer network transmission media. The size of the reflected signals is indicative of the size of the impedance discontinuity, and the delay between the generation of the TDR signal and the detection of the reflection is indicative of the distance to the discontinuity based upon the round-trip signal travel time.
In the past for data networks, time domain reflectometry techniques have been essentially qualitative in nature. The voltage magnitude of the reflected signals was used as a gross measure of the size of the impedance discontinuity, and the distance to the discontinuity could be measured. Other parameters such as attenuation could be estimated by electrical signal measurements only when the physical length of the link was known.
The present invention is directed to a method and system for computer network physical layer analysis. It uses signal analysis techniques and begins with time-domain responses to yield highly quantitative analysis of the computer network""s physical layer. Moreover, it enables the isolation of the response of a desired section of the computer network, including the removal of the contribution of portions of the network that are not under analysis and/or computer network communication devices such as hubs. This facilitates targeting of the node-side of the computer network, which is most susceptible to physical damage and unauthorized modification, but is also relevant to cable and installed-network validation.
In general, according to one aspect, the invention features a method for computer network physical layer analysis. The method includes detecting transmissions on a computer network link including instantaneous voltage levels on a computer network media of the link. Multiple transmissions are accumulated into a composite response of the computer network link. This composite response is then used as the basis for analysis of the computer network link.
In the preferred embodiment, the step of accumulating multiple transmissions comprises accumulating at least ten transmissions into the composite response prior to the step of analyzing the computer network link using the composite response. Preferably, the transmissions are a predetermined signal that is generated on the computer network link.
To facilitate further analysis, a response of a network communications device maintaining the network communications link is preferably detected. Here again, a composite response is preferably formulated.
Analyses such as the calculation of the resistance and an impedance as a function of frequency of the computer network media from the composite response are preferably performed, including corrections for accumulated resistivity of the network transmission media. Typically, in the context of a fully configured link, a response of a network communications device maintaining the network communications link is preferably detected.
Crosstalk can also be measured by stimulating one wiring pair and measuring a response to the stimulus on another wiring pair of the network communications link. Here again composite responses are preferably generated to increase precision of the measurement. In one embodiment, the wiring pairs are stimulated with a Walsh Hadamard function.
In general, according to another aspect, the invention also features a system for computer network physical layer analysis. The system includes a digitizer for detecting transmissions on a computer network link including instantaneous voltage levels on a computer network media of the link and a controller for accumulating multiple detected transmissions into a composite response of the computer network link and analyzing the computer network link in response to the composite response.
In general, according to another aspect, the invention also features a method for computer network physical layer analysis. This method includes generating a predetermined signal on a computer network link. A response of the computer network link to the predetermined signal is then detected and analyzed for indicia of a termination using at least two different criteria preferably by a controller. The results of the analysis are then compared to characterize the termination. This is useful where the type of termination is not known, a priori, but the analysis is automated.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.